Since the causative agent of Lyme disease can cross the placenta and infect the fetus, maternal infection theoretically poses a risk to the normal growth and development of the fetal heart. The purpose of the proposed work is to determine the nature and extent of the relationship between prenatal Lyme disease and congenital heart disease and to identify any modifying factors that decrease existing risks. The specific aims are: 1) to estimate the risk of congenital heart disease associated with either pre- or post conception maternal Lyme disease as defined by clinical history and/or a positive Lyme titer; 2) to determine if tick bites in the absence of a clinical history of Lyme disease increase the risk of congenital heart disease; 3) to determine if residence in a highly endemic area in the absence of a known clinical history of Lyme disease is associated with an increased risk of congenital heart disease; 4) to examine the role of maternal treatment for Lyme disease or a tick bite as a potential factor that can modify existing risks; and 5) to learn more about the pathogenesis underlying any existing association by looking at specific cardiac abnormalities. This is a retrospective case-control study. The cases will be comprised of 875 children who reside in a Lyme endemic area and who were diagnosed as having a congenital heart abnormality before 5 years of age at Westchester County Medical Center from 1988-1994. The control group will be selected from among patients who were seen at the medical center for evaluation and were subsequently diagnosed as normal. The control group will be comprised of 875 of these children or their siblings. The mothers of cases and controls will complete a mailed questionnaire which will include questions about Lyme disease exposure, as well as sections on reproductive history and maternal characteristics and habits. Additional data on Lyme disease exposure will be obtained through medical records and through serologic testing of the children who might have been exposed in-utero and their mothers as well as mothers and children who live in towns where Lyme disease is highly endemic. Logistic regression analysis will determine if the children with congenital heart disease are more likely than controls to have a mother who was at increased risk of exposure to Lyme disease either before or during her pregnancy. The models will include Lyme-related variables as well as other variables that could be associated with congenital heart disease.